September 12, 2012

Female Pit Vipers Give Birth Without Mating

In what could be the ultimate act of feminism, wild female North American pit vipers have been shown to give birth without mating, according to a new report published in the Royal Society's Biology Letters.

A phenomenon, known as facultative parthenogenesis (FP), has been observed in captivity before and the report asserts that it can occur regardless of the presence of male individuals.

“In these populations, males are relatively common, hence females were not restricted from access to males, and therefore isolation from males is not a driving factor for parthenogenic reproduction (virgin births) here,” lead author Warren Booth, a biologist at the University of Tulsa told Discovery News.

To study this phenomenon, Booth and several colleagues field-collected two closely related species of pregnant pit vipers, the copperhead and the cottonmouth, where males were present in the local ecosystems.

Of the 59 litters produced by the snakes, the scientists selected two for DNA analysis, which were produced by individuals that had already showed tell-tale signs of virgin birthing, including eggs that had multiple yolks and the litters with a single male offspring. The researchers then conducted a genetic analysis, which showed that one copperhead and one cottonmouth had delivered a virgin birth.

"I think the frequency is what really shocked us," Booth said."That's between 2.5 and 5 percent of litters produced in these populations may be resulting from parthenogenesis.”

"That's quite remarkable for something that has been considered an evolutionary novelty," he added.

According to Booth, in each incidence of pit viper FP–the female´s egg cell “fused to a part of itself, and her chromosomes doubled”, resulting in offspring that had two copies of the female´s chromosomes and therefore half the genetic material.

“This means she has very reduced diversity across her genome,” he said. “This is essentially an extreme form of inbreeding.”

This discovery added to the number of species know for FP that includes 10 species of snakes, four species of shark, and several monitor lizards, including the Komodo dragon, which is considered endangered and already suffering from a lack of genetic diversity.

However, the previous members of this group were kept in isolation in unnatural conditions and away from any males.

The researchers expressed concern that a resulting loss of diversity due to FP can lead to genetic maladies being spread throughout a population. However, Booth noted that diversity loss does not affect all species equally.

“We see extreme inbreeding in many insect species, such as bed bugs and cockroaches, and they thrive. So while inbreeding is never ideal, it is not necessarily bad in all cases,” he said.

Scientists currently believe that FP is more common in some lineages such as reptiles and sharks and unlikely to come from placental mammals, which would undoubtedly stir up some controversy in Christian religious circles.

Since mammals require the interaction between the two sets of parental genes for a process called genomic imprinting, any mammalian embryos that could possibly result from FP would not develop normally.

According to Booth and his colleagues, future research on FP should focus on the reproductive competence of these virgin births and population genetics modeling of these individuals.